Various ultrahigh temperature heating systems have heretofore been utilized; however, because of certain inherent structural features they have been beset with one or more of the following shortcomings: (a) it was difficult to maintain a proper liquid seal within certain portions of the system thereby resulting in a loss of steam or an ineffective condensing of the steam within the product prior to the latter being received in a holder tube; (b) approval of the system by various public health authorities for pasteurization of the product was denied because of the inconsistency or instability of the product entering the holder tube (i.e., steam would occupy space normally occupied by the product) and also because of variations in liquid flow whereby the necessary hold time to effect pasteurization could not be accurately determined; and (c) because the steam entrained in the product was not completely condensed prior to entering the holder tube, the noncondensed steam would collapse within the holder tube creating serious mechanical shocks to occur throughout the system thereby resulting in an inordinate amount of damage to various components or premature failure of various fittings.